The present invention relates to a method for the economical production of non-toxic biomass through a high density symbiotic culture between microalgae and fishes, in which fishes provide dissolved carbon dioxide, inorganic nitrogen, physical agitation, and removal of contaminated protozoa benefical to the microalgae, while microalgae provide dissolved oxygen, nutrients, and consumption of excreted compounds to clean the water beneficial to the fishes.
Since the 1960's much attentions and extensive efforts have been devoted to the production of single cell protein (SCP) to solve the increasing problem of world food shortage. However, the high production cost has always excluded SCP products from the feed market. Toxicological concern relating to petroleum-based SCP is also problematic for products to be accepted as feed or food. Attempts to produce microalgal dry biomass containing about 50% protein had been initiated even earlier than those for bacterial or yeast SCP. Again the high production cost has discouraged the microalgal food programs, and recently the general research trend toward microalgal production appears to have shifted from the production of low value --high volume products to the production of high value --low volume products including pharmaceutical and specialty chemicals.
The high cost of carbon dioxide accounts for the main part of the production costs for microalgal biomass. Costs for agitation, recovery of cells, nitrogen sources, and minerals should be also included in the production costs. In a large-scale outdoor culture of microalgae, contamination and overgrowth of protozoa often cause serious problems.